A kidney stent, more accurately called a ureteral stent, is a thin, flexible tube temporarily placed inside the body’s urinary system. This small medical device maintains the flow of urine from the kidney to the bladder through the ureter. It is a hollow tube that prevents blockage and allows the kidney to drain properly. The stent is completely internal and not visible from the outside unless a specific type with a retrieval string is used.
Anatomy and Design of a Kidney Stent
The most common type of kidney stent is known as a double J stent or pigtail stent, named for its distinctive shape. This tube is typically made from a flexible, medical-grade polymer, such as polyurethane or silicone, which allows it to bend with the body’s movements. The soft, smooth material is designed to minimize irritation to the delicate lining of the ureter.
The stent itself is a hollow catheter with multiple small side holes along its length to facilitate urine drainage, both through the center of the tube and around it. For an adult patient, the length of the stent generally varies, falling in a range between 24 and 30 centimeters (about 9.5 to 12 inches). Its diameter, or gauge, is measured in French units (Fr), with common sizes ranging from 4.7 Fr to 8 Fr, which corresponds to a width of only a few millimeters.
The defining feature of this stent is the curled shape at both ends, which gives it the “double J” or “pigtail” appearance. These curls are engineered to sit securely within the body, one in the renal pelvis of the kidney and the other in the bladder. This coiled design prevents the stent from migrating up toward the kidney or slipping down entirely into the bladder, which is necessary for its function.
Some shorter-term stents are manufactured with a thin, fine string attached to the end that rests in the bladder. This retrieval string exits the body through the urethra and is sometimes taped to the skin. The presence of this string allows for easier removal without requiring a second procedure.
Medical Necessity and Anatomical Placement
The primary function of a kidney stent is to restore or maintain the flow of urine when the ureter is obstructed or at risk of obstruction. If urine cannot drain from the kidney, pressure builds up, a condition called hydronephrosis, which can lead to infection and kidney damage over time. The stent acts as an internal splint to bypass the blockage and protect the kidney’s function.
Common medical reasons for placement include:
- Kidney stones blocking the ureter, or swelling and trauma following stone removal procedures.
- Scar tissue.
- Tumors pressing on the ureter from the outside.
- Procedures that have caused narrowing of the ureter.
By keeping the ureter patent, the stent allows the body’s natural passageway to heal after an injury or surgery.
Anatomically, the stent is placed along the entire length of the ureter, the muscular tube that connects the kidney to the bladder. The upper curl is situated in the renal pelvis, and the lower curl is positioned inside the bladder. This placement ensures a continuous, open channel for urine to pass from the filtering organ to the storage organ.
The Insertion and Removal Process
Stent insertion is most often performed using a technique called cystoscopy, which is typically an outpatient procedure. The patient is given anesthesia or sedation, and the physician uses a cystoscope—a thin, flexible tube equipped with a camera—to enter the bladder through the urethra. This allows the doctor to visually identify the opening of the ureter.
A thin guide wire is then advanced through the cystoscope and up into the ureter, reaching the kidney. The kidney stent is threaded over this guide wire and carefully pushed into position. Imaging techniques, such as fluoroscopy (real-time X-ray), are frequently used during the placement to confirm the correct positioning of the curls. Once the stent is correctly seated, the guide wire and cystoscope are removed, leaving the stent in place.
The method for removing the stent depends on whether a retrieval string was utilized during insertion. If a string is present, the removal is simple and fast, often performed by the patient at home or by a healthcare provider in a clinic setting by gently pulling on the exposed string. If no string was left, the stent is removed using a second, minor cystoscopy procedure.
For a cystoscopic removal, the doctor inserts the flexible scope into the bladder to visualize the coiled end of the stent. A specialized grasper or forceps is passed through the scope to grasp the coil. The stent is then gently pulled out as the scope is removed, a process that is usually very quick, taking only a minute or two.